In recent years, flat panel display devices that use flat panel display elements such as liquid crystal panels and plasma display panels are increasingly used as display elements for image display devices such as television receivers instead of conventional cathode-ray tube displays, allowing image display devices to be made thinner. In the liquid crystal display device, a liquid crystal panel used therein does not emit light, and therefore, it is necessary to separately provide a backlight device as an illumination device. Backlight devices are largely categorized into a direct-lighting type and an edge-lighting type depending on the mechanism thereof. Edge lit backlight devices include a light guide plate that guides light emitted from light sources disposed on the edge, and an optical member that applies optical effects on the light from the light guide plate and supplies the light as even planar light to the liquid crystal panel, and one known example thereof is the matter disclosed in Patent Document 1 below. Patent Document 1 discloses a configuration in which a light guide plate has a light focusing function by arranging a plurality of cylindrical lenses on the light-exiting surface of the light guide plate, and a prism sheet is disposed on the light-exiting surface.